text: Bronze technology was imported to China from the steppes. The oldest bronze object found in China was a knife found at a Majiayao culture site in Dongxiang, Gansu, and dated to 2900–2740 BC. Further copper and bronze objects have been found at Machang-period sites in Gansu. Metallurgy spread to the middle and lower Yellow River region in the late 3rd millennium BC. Contacts between the Afanasievo culture and the Majiayao culture and the Qijia culture have been considered for the transmission of bronze technology. From around 2000 BCE, cast bronze objects such as the socketed spear with single side hook were imported and adapted from the Seima-Turbino culture.
  The Erlitou culture (c. 1900 – 1500 BCE), Shang Dynasty (c. 1600 – 1046 BCE) and Sanxingdui culture (c. 1250 – 1046 BCE) of early China used bronze vessels for rituals (see Chinese ritual bronzes) as well as farming implements and weapons.  By 1500 BCE, excellent bronzes were being made in China in large quantities, partly as a display of status, and as many as 200 large pieces were buried with their owner for use in the afterlife, as in the Tomb of Fu Hao, a Shang queen.
  In the tomb of the first Qin Emperor and multiple Warring States period tombs, extremely sharp swords and other weapons were found, coated with chromium oxide, which made the weapons rust resistant. The layer of chromium oxide used on these swords was 10 to 15 micrometers and left them in pristine condition to this day. Chromium was first scientifically attested in the 18th century.
  The beginning of new breakthroughs in metallurgy occurred towards the Yangzi Rivers south in Chinas southeastern region in the Warring States Period such as gilt-bronze swords.